Mean Bond Energy Research Articles

Effect of Ge-addition on physical and optical properties of chalcogenide Pb10Se90-xGex bulk glasses and thin films

Several substantial physical and optical properties of non-crystalline Pb10Se90-xGex bulk glasses and thin-films (0.0 ≤ x ≤ 10 at.%) have been studied. Bulk and film samples were synthesized via melt-quench and thermal-evaporation processes, respectively. The films were fabricated on pre-cleaned glass substrates under vacuum ≈5 × 10−4 Pa. The non-crystallinity of studied samples has investigated by X-ray diffractograms. A good-matching between selected compositional elements and those measured experimentally was confirmed by energy-dispersive X-ray analysis. The absorption nature of samples was studied in detail, where absorbance, absorption coefficient, skin depth and skin effect were discussed. The indirect transition bandgap energy was studied and its value decreases as Ge-content increases. Cohesive energy, average coordinate number, average atomization heat, lone-pair electrons, mean-bond energy, and others were discussed. Based on density values, many parameters were estimated and studied, like compactness, packing density, atomic densities, polaron radius, field strength. All studied characterizations are strongly dependent upon Ge-percentages.

Investigation of the correlation between physico-chemical, optical and thermal properties of (GeS2)60(Sb2S3)40−x(CdCl2)x chalcohalide glasses

The correlation between physico-chemical, optical, and thermal properties of (GeS2)60(Sb2S3)40−x(CdCl2)x (x = 0, 10, 20, 30, and 40 mol%) chalcohalide glasses was systematically investigated through the replacement of Sb2S3 by CdCl2. The optical band gap was estimated based on the system density, and it was turned out that it hardly increased from 2.16 to 2.3 eV with increasing CdCl2 content from 0 to 40 mol%. Moreover, we theoretically determined the valence band (EVB) and conduction band (ECB) positions using the calculated band gap values. The molar volume of the studied system increased while the density as well as the packing density decreased by increasing CdCl2 content. The average coordination number, the constraints number, the mean bond energy, and the average heat of atomization have been calculated via the chemical bond approach and have been found to decrease when the CdCl2 content increases. On the other hand, the number of lone-pair electrons and the cohesive energy have been found to increase. Finally, the variation of the glass-transition temperature was also discussed in terms of the overall mean bond, and it was found to decrease with increasing CdCl2 content.

On the structural and thermophysical study of Pb-doped Se-Te-In nanochalcogenide alloys

ABSTRACT Pb additive nanochalcogenide materials are becoming well-known materials in modern optoelectronics. In this paper, multicomponent Se-Te-In-Pb nanochalcogenide alloys are prepared using melt-quenching technique. The physical and submicron structural features of investigated system are reported and discussed. Characteristic peaks in x-ray spectra signify nanorange of each sample under investigation validated by FESEM and HRTEM. Influence of Pb content on examined composition has been deliberated with respect to their physical characterization namely average coordination number (<r>), mean bond energy (<E>), cross-linking density (X), lone-pair electrons (L), fraction of floppy modes (f), constraints (Nc ), electronegativity (χ), cohesive energy (CE), glass transition temperature (Tg ), and heat of atomization (Hs ). It is realized that addition of Pb content, enhanced Nc, X, and <r>. Whereas, <E>, L, f, χ, CE, Tg , and Hs decrease with Pb addition. Cohesive energy is analyzed through chemical-bond approach. Tg is estimated by Tichy-Ticha and Lankhorst approaches and are found in consistent with experimental results. The band gap of investigated system has been calculated theoretically by Shimakawa’s relation and deduced results are analyzed through cohesive energy, electronegativity, and average single-bond energy. Also the compositional dependence of experimentally derived optical band gap has been analyzed and discussed.

The effect of substitution of Sb with Zn on the optical and physical properties of Se90Sb10-xZnx (x = 0, 2, 4, 6, 10 at. %) thin films

In the present study, the effect of substitution of Sb with Zn on the optical properties of Se90Sb10-xZnx (x = 0, 2, 4, 6, 10 at. %) thin films is discussed. Bulk samples are prepared using a conventional melt-quench technique. Amorphous thin films of the compositions are synthesized using thermal evaporation technique. Normal incidence transmission spectra of films is obtained in the spectral range of 400–1100 nm. The envelope method is applied to calculate the refractive index, followed by Cauchy's extrapolation. Spectral distributions of extinction coefficient, absorption coefficient and dielectric loss factor are obtained. Wemple-Didomenico single oscillator model is employed to study refractive index dispersion. The absorption coefficient is of the order of 104 cm−1, and the band-gap is calculated using Tauc’s extrapolation for the indirect transition. The increase in band gap with Zn addition is explained on the basis of chemical bond approach. Topological studies show that the system is in a rigid region The glass transition temperature, mean bond energy and density of the system is also increasing with the increase in Zn content. An effort is made to discuss all the parameters in terms of change in bond length, bond energy and connectedness of the glassy network.

EFFECT OF COMPOSITIONAL VARIATION ON PHYSICAL PARAMETERS OF QUATERNARY CHALCOGENIDE GLASSES Se69Sn10Ge21-xSbx (6≤x≤14)

The glassy alloysSe69Sn10Ge21-xSbx (where x= 6, 8, 10, 12, 14) are prepared by melt quench technique. The physical parameters have been studied such as average coordination number, number of constraints, floppy mode, Lone pair electron, mean bond energy and glass transition temperature etc.The chemical bond approach has been used to calculate cohesive energy of the samples. The mean bond energy and glass transition temperature has been calculated using Tichy-Ticha Approach. It has been observed from the study that with addition of Sb, the parameters such as average coordination number, mean bond energy and glass transition temperature decreases.

Physical and optical properties of a-Ge-Sb-Se-Te bulk and film samples: Refractive index and its association with electronic polarizability of thermally evaporated a-Ge15-xSbxSe50Te35 thin-films

This work is dedicated to the deduction of many basic physical parameters of a-Ge15-xSbxSe50Te35 bulk and thin-film samples, GSST (0.0 ≤ x ≤ 15.0 at.wt.%). Besides, study the interrelationships among refractive index, molar refractivity and electronic polarizability of these film samples. Solid-state solutions of GSST compositions were prepared followed by melt-quenching method to get the glassy bulk samples. The thin-film samples of thickness 200 nm were fabricated by thermal evaporation technique. X-ray diffractograms revealed that all prepared GSST bulk and film samples are of non-crystalline nature. The ingots bulk Ge-Sb-Se-Te samples have been used to practically estimate the density. The refractive index of Ge15-xSbxSe50Te35 amorphous thin-films have been utilized to discuss the electronic polarizability, Covalence parameter and optical electronegativity. As well as, the deviation from stoichiometry, average heat of atomization, the overall mean bond energy and the glass transition temperature are also evaluated. All studied parameters are highly dependent on the Sb-ratio.

Study of glass-forming ability and structural rigidity of Zn-modified (GeTe)x(Sb2Te3)100−x chalcogenide glassy alloys

ABSTRACTTelluride-based phase-change chalcogenide alloys have utmost importance in memory applications due to their ultrafast switching between amorphous to microcrystalline and vice versa. The present study reports the compositional-dependent physical parameters of Zn modified (GeTe)x(Sb2Te3)100−x chalcogenide phase-change alloys to explicate their glass-forming ability and memory switching properties in terms of expected presence of chemical bonds. The theoretical estimation of physical properties of GeTe, Ge8Sb2Te11, Ge2Sb2Te5 and Sb2Te3 phase-change chalcogenide alloys and comparison of effects of Zn doping in the alloys have been carried out. These include average coordination number, number of lone pair electrons, deviation of stoichiometry, electronegativity and overall mean bond energy. The glass transition temperature of Zn-modified (GeTe)x(Sb2Te3)100−x alloys has been estimated by the model presented by Lankhorst and cohesive energy (CE) of the systems is calculated using chemical bond approach model. A linear relation is found between CE and the heat of atomization for all compositions.

Mechanical and electrical properties of As-Se glasses

The current study focused on the impact of arsenic additions on the mechanical, and electrical properties of binary As-Se glasses. Different elastic parameters such as micro-hardness (H), Poisson's ratio (σ), Young (Y)-, and bulk (K)-moduli) as well as Debye temperature (TD) for As-Se glasses were determined based on the measured values of the ultrasonically speeds (transfer, vl, and shear, vs). The activation energies for electrical (ΔEdc) and for thermoelectrical conduction (ΔEthermo) of these glassy thin films were investigated as a function of composition. Y, K and ΔEdc were correlated with the glass transition temperature (Tg). The obtained results were discussed in terms of the average coordination number, crosslink density and overall mean bond energy.

The influence of dopant atoms introduction on some thermal, optical and structural parameters of Bi(As2S3)100−X Glassy system

Paper presents the results of analysis of several experimentally obtained physical parameters of Bix(As2S3)100−x glassy system from the topological point of view. The dependence on composition of the glass transition temperature was explained with increase in total number of mechanical constraints and based on Tanaka′s relation. The compound with the highest content of Bi showed an exception from observed behavior due to its structural complexity. Its heterogenity also reflected on the flow of thermal decomposition process. The reduction of the optical band gap was correlated with the decrease of system cohesive energy. The observed minimum of compactness for the compound with x = 5 at.% of Bi is probably caused by Tanaka’s 2D → 3D transformations. The decrease of the mean bond energy was interpreted as a consequence of formation of weaker Bi-S bonds instead of As-S bonds, and the formation of homopolar bonds between residual As atoms in excess.

Topological behavior and glassy framework of GeTeSeGa chalcogenide glasses

Te-based chalcogenide glasses own the most comprehensive infrared window among amorphous materials and have far-infrared applications such as CO2 detection. Nevertheless, the glass forming ability and thermal stability decrease for higher Te content chalcogenide glasses. Here, we report the effect of Ga addition on Te-based chalcogenide glasses by presuming that the addition of Ga may develop the configurational disorder and hence may improve the glass forming ability and thermal stability. Ge10Te80Se10-xGax (x = 0, 2, 4, 6, 8, 10 at %) bulk chalcogenide glassy alloys have been synthesized via melt quench technique. The role of Ga is studied through a semi-empirical approach. The result shows that the system is in rigid mode (total number of mechanical constraints >3). The density of the system shows an increase which is further supported by a decrease in free volume percentage. Mean bond energy and glass transition temperature have also been investigated. The energy gap shows a decrease with increase in Ga at. % and the behavior are correlated with the decrease in average single bond energy (72.7 kJ/mol to 69.7 kJ/mol) and electronegativity (2.14–2.06) of the system. From the results of covalent character (>90%), it is estimated that the compositions may be used to form stable glasses, which may be helpful in the development of an infrared system.

Physical properties of third generation multicomponent Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) chalcogenide glasses

Abstract Selenium-based chalcogenide glasses are best suitable materials for optical data storage due to their amorphous-to-crystalline phase transformation. Average coordination number and number of constraints for Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) system have been discussed with two topological effects, floppy and rigid transition. Mean bond energy and glass transition temperature have been investigated using chemical bond approach to understand structural features of glasses. Heat of atomization, mean bond energy and glass transition temperature have been studied theoretically.

Influence of Cu content on physical characterization and optical properties of new amorphous Ge–Se–Sb–Cu thin films

The present work aims to theoretically study the effect of Cu concentration through many physical parameters, including coordination number (CN), constraints number (CON), overall mean bond energy and cohesive energy (CE), for Ge25Se65Sb10−xCux (where x = 0, 2.5, 5, 7.5 and 10 at%) glasses. As well, the optical constants of the thin films were evaluated via the use of the Swanepoel technique. As the Cu concentration rises, it is found that CN, CON, and CE also rise. This relationship demonstrates the obvious evidence for incremental rigidity of the Ge25Se65Sb10−xCux glasses with the addition of Cu. The chemical bonds anticipated within the glasses were estimated. It was revealed that the heteropolar bonds occurred in the examined glasses are Cu–Se, Ge–Se and Sb–Se, which have energies of 62.425, 49.441 and 43.981 kcal mol−1, respectively. The acquired estimations of the refractive index (n) of the films were fitted to the two-term Cauchy dispersion equation to get the single oscillator (Eo) and dispersion (Ed) energies. In addition, the estimations of the absorption coefficient (α) were acquired using the conditions suggested by Connell and Lewis. An energy gap (Eg) decrement from 1.79 to 1.47 eV was prompted by a Cu concentration rise from 0 to 10% at%.

Investigation of Some Physico-Chemical Properties in Multi-Component Se–Te–Sn–Sb (0 ≤ x ≤ 6) Quaternary Chalcogenide Glassy System

In the present work we report physico-chemical properties in novel Se78 – xTe20Sn2Sbx (x = 0, 2, 4 and 6) glassy system prepared by melt quench technique. Various physico-chemical properties such as co-ordination number, lone pair of electrons, number of constraints, density, molar volume, compactness, mean bond energy, cohesive energy, glass transition temperature and covalence character has been estimated. The compositional dependence of aforesaid physico-chemical properties has been investigated. It has been observed that average number of constraints, mean bond energy, glass transition temperature are found to increase where as number of lone pair of electrons and electro negativity decreases with increases of Sb content in the Se78 – xTe20Sn2Sbx (x = 0, 2, 4 and 6) glassy alloys.

Analysis of glass forming ability using percolation concept and tunability of physical parameters of a-Ge12Se76-xAs12Bixglassy semiconductors

AbstractGlass forming ability of lone-pair semiconductors was analyzed for (x = 0, 2, 4, 6, 8, 10) system. Values of lone pair electrons L were calculated using average coordination number of valence electrons. These values were found to decrease, as the system was moving towards the rigid region. L &gt; 3 values showed vitreous state. Deviation of the stoichiometry confirmed the chalcogen-rich region. A linear correlation was found between the mean bond energy and glass transition temperature. Chemical Bond Approach model was applied to calculate the cohesive energy of the system. A linear relationship was found to exist between the cohesive energy and the theoretical band gap, calculated using Shimakawa relation. A decrease in both parameters was explained on the basis of average stabilization energy and electronegativity of the system. The density values were found to increase and may account for higher refractive index of the system. Large Bohr radius of the Bi atom accounted for an increase in the polarizability. Other parameters viz. degree of covalency, packing density, compactness, molar volume, free volume percentage, excess volume and polaron radius were also calculated. An effort was made to correlate the effect of Bi addition to Ge12Se76-xAs12Bixlone-pair semiconductor on the basis of the structure of the glassy matrix or the connectedness of the material.

Crystallization kinetics of binary arsenic selenium chalcogenides

Binary As–Se glasses with different amounts of As content have been prepared and scanned with different heating rates (3 ≤ ψ ≤ 48 K min−1) over temperatures ranging from 300 to 450 K. Both the glass transition temperature (Tgl) and the temperature peak of crystallization (Tpc) increase as a function of As and/or the ψ values. A good correlation between Tgl and Tpc has been investigated. The observed increase in Tgl and Tpc by increasing the ψ values or as a function of As is well discussed in accordance with Lasocka’s relationship and using the average coordination number Acn, the viscosity at glass transition μ(Tgl) and the overall mean bond energy E. The glass transition Egl and crystallization activation energies (Egl and Epc) were determined based on the changes in Tgl and Tpc values due to the heating rate (ψ). The increase in the values of Egl and Epc with increasing the As content is expected due to the increase in Tgl and Tpc values. The kinetic exponent n and the crystal dimensionality m have been determined.

Optical parameters of Ge15Sb5Se80 and Ge15Sb5Te80 from ellipsometric measurements

The optical properties of Ge15Sb5Se80 (GSS) and Ge15Sb5Te80 (GST) films prepared by thermal evaporation method were investigated in the photon energy range from 0.9 eV to 5 eV by using a variable-angle spectroscopic ellipsometer. Combinations of multiple Gaussian, and Tauc–Lorentz or Cody-Lorentz dispersion functions are used to fit the experimental data. The models' parameters (Lorentz oscillator amplitude, resonance energy, oscillator width, optical band gap, and Urbach energy) of both GSS and GST films were calculated. Refractive indices and extinction coefficients of the films were determined. Analysis of the absorption coefficient shows that the optical absorption edge of GSS and GST films to be 1.6 eV and 0.89 eV, respectively. Manca's relation based on mean bond energy and the bond statistics of chemically ordered model (COM) and random covalent network model (CRNM) is applied for the estimation of the optical band gap (Eg) of the investigated films. A good agreement between experimental and calculated Eg is obtained.

Glass transition kinetics aspects of amorphous Se60Ge15As25 and Se60Ge15Sn25 compositions

This work aims to research the glass transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Glass transition temperature (T g) has been discovered heating rate and composition dependence. Composition reliance of T g can be comprehended with the correlation between T g and coordination number and mean bond energy also for the investigated compositions. Heating rate dependence of T g reveals the activation energy of glass transition (E g) values according to various methods for T g with various definitions. The estimated E g values have been discovered enlarging with temperature throughout the glass transition region. The relative error (e %) for Kissinger’s activation energy and its related parameters have been resolved and discussed. The correlation between glass transition and crystallization temperatures reveals that the crystallization process is more sensitive to heating rate than glass transition process. The critical heating rate value reflects that the Se60Ge15As25 composition is the most thermal stable composition. Fragility index values have been assessed by various relations and categorized the compositions under review as strong glasses.

New amorphous As–Se–Sb–Cu thin films: theoretical characterization and evaluation of optical constants

The purpose of this paper is to report the theoretical characterization and optical constants of the newly As30Se55Sb15-x Cu x (where x = 2.5, 5, 7.5 and 10 at%) thin films. Amorphous thin films were prepared from As30Se55Sb15-x Cu x ingots utilizing the thermal evaporation technique. The average coordination number, the number of constraints, the overall mean bond energy, the average heat of atomization, and the cohesive energy were examined theoretically. The optical transmission spectra for the as-prepared films have been measured in the spectral range from 400 to 2500 nm at normal incidence. Swanepoel method was utilized to obtain the refractive index and thickness of the As30Se55Sb15-x Cu x thin films. The absorption coefficient of the investigated films was calculated using the Connell and Lewis equation. It was found that the refractive index and the extinction coefficient of As30Se55Sb15-x Cu x films are influenced by increasing the copper content. Increasing the Cu content from 2.5 to 10 at% leads to a decrease of the energy gap from 1.61 to 1.42 eV.

Physical and optical properties of bulk and thin films of a–Ge–Sb–Te lone-pair semiconductors

ABSTRACTPhysical parameters and their correlation with optical band gap and refractive index for amorphous Ge20Te80-xSbx (x = 0, 2, 4, 6, 8, 10) lone-pair semiconductors were discussed. Using average coordination number lone-pair electrons (L) were calculated and found to decrease with an increase in the Sb content. However, L value greater than 3 indicated that Ge20Te80-xSbx alloys can retain their vitreous nature. The density of alloys was measured both experimentally and theoretically. Increased density values with the increase of Sb content further accounts for the concurrent increase in the refractive index values. The results were explained on the basis of increased polarizability and larger Bohr radius of Sb. Compactness of the structure was found to decrease with the alterations of the atomic arrangements. Molar volume (calculated from the measured density values) found to decrease with Sb content. The number of atoms per unit volume (N) was calculated, using molar volume and average coordination number and were found to increase. This increase in N accounts for the decrease in the optical band gap. Other optical parameters viz. optical density, penetration depth and Urbach energy were also calculated. An increase in Urbach energy showed the reduction in band tail width with increased defect concentration. Positions of the conduction bands and valence bands were found to shift towards the Fermi edge, which accounts for the reduction in the optical band gap. Chemical bond approach (CBA) model was applied to estimate the cohesive energy of the system and found to decrease with the Sb content. A linear relation is found between the behaviour of cohesive energy and band gap (calculated both experimentally and theoretically). Deviation of stoichiometry confirmed chalcogen-rich region for all the compositions. The mean bond energy was found to be proportional to the glass transition temperature and showed maxima at the chemical threshold. The obtained results were discussed in terms of average coordination number or equivalently structure of the glassy matrix, decrease in average stabilization energy, electronegativity and average heat of atomization of the system. In amorphous materials, maximum optical non-linearity has been predicted. To open the prospects of Ge–Te–Sb vitreous system for non-linearity, Sheikh and Bahae relationship was applied, using experimentally obtained parameters, at a telecommunication wavelength. Obtained results showed a decent agreement with values available in the literature at 0.8 eV or 1550 nm. Non-linear refractive indices, almost three orders higher than silica glass, were obtained. These results may lead to yielding more sensitive optical limiting devices, and these glasses may be used as an optical material for a high-speed communication fibre.

Dirac-Fock-Breit-Gaunt calculations for tungsten hexacarbonyl W(CO)6.

The first all-electron fully relativistic Dirac-Fock-Breit-Gaunt (DFBG), Dirac-Fock (DF), and nonrelativistic (NR) Hartree-Fock (HF) calculations are reported for octahedral (Oh) tungsten hexacarbonyl W(CO)6. Our DF and NR HF calculations predict atomization energy of 73.76 and 70.33 eV, respectively. The relativistic contribution of ∼3.4 eV to the atomization energy of W(CO)6 is fairly significant. The DF and NR energy for the reaction W + 6CO → W(CO)6 is calculated as -7.90 and -8.86 eV, respectively. The mean bond energy predicted by our NR and DF calculations is 142.5 kJ/mol and 177.5 kJ/mol, respectively, and our predicted DF mean bond energy is in excellent agreement with the experimental value of 179 kJ/mol quoted in the literature. The relativistic effects contribute ∼35 kJ/mol to the mean bond energy and the calculated BSSE is 1.6 kcal/mol, which indicates that the triple zeta basis set used here is fairly good. The mean bond energy and the atomization energy calculated in our DFBG SCF calculations, which include variationally both the relativistic and magnetic Breit effects, is 157.4 kJ/mol and 68.84 eV, respectively. The magnetic Breit effects lead to a decrease of ∼20 kJ/mol and ∼4.9 eV for the mean bond energy and atomization energy, respectively, for W(CO)6. Our calculated magnetic Breit interaction energy of -9.79 eV for the energy of reaction (ΔE) for W + 6CO → W(CO)6 is lower by ∼1.90 eV as compared to the corresponding DF value (ΔE) and contributes significantly to the ΔE. A detailed discussion is presented of electronic structure, bonding, and molecular energy levels at various levels of theory for W(CO)6.